Control apparatus for reversible motors



Feb. 18, 1947, M. G. sHoEMAKER CONTROL APPARATUS FOR REVERSIBLEMOTOHS Filed Feb. 26, 1944 SSE i mwa Patented Feb. 18, 1947 CONTROL APPARATUS FOR REVERSIBLE MOTORS Malcolm G. Shoemaker, Abington, Pa., assignor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application February 26, 1944, Serial No. 524,097

14 Claims. l

This invention relates to an improved electric motor reversing system. More particularly, it relates to a system for reversing the operation of an electric motor driven mechanism, suchas the scanning antenna employed in radio detecting and ranging (radar) systems and the like.

It has heretofore been proposed to reverse the operation of such mechanism by a continuously rotating commutator type switching means employing an adjustable brush to positively vary the relative periods of forward and reverse rotation and to compensate for creep inherent in reverse operation of electric motor driven mechanisms. Such device is disclosed and claimed in the copending application of F. R. Farrow, Serial No. 520,307, filed January 29, 1944.

It is an object of my invention to provide an improved reversing system employing a simplified device for controlling the periods of -forward and reverse operation.

Another object of the invention is to provide, in a system of the above type, for the making and breaking of the reversing circuit at contacts other than those which determine the periods of forward and reverse motion, whereby more effective design of the individual units and of the whole system may be possible and more satisfactory operation may result.

Another object of the invention is to improve the operation and lengthen the life of apparatus of the above type' by assigning to a switching device, particularly suited therefor, the function of making and breaking the circuit to the controlled motor; and assigning the function of control of the periods of reversal to another device whose construction is particularly suitable thereto.

Other objects and advantages will appear as the invention is described in connection with the drawing.

The single figure of the drawing illustrates diagrammatically a system embodying the invention.

In the drawing, a motor 2 is provided to rotate or oscillate a mechanism such as a directional antenna, or other device, over which control of the speed of rotation and period of oscillation is desirable. In radar practice such devices are commonly known as spinners or scanning devices, and such device is so designated in the drawing where itis represented diagrammatically by the circular figure bearing the reference numeral 4. Since the structure and operation of such apparatus is known, and may vary according to the use to which it may be applied, the particular apparatus driven by the motor 2 is not specifically illustrated nor described in detail herein. It will be sumcient to mention that motors generally do'not run equally well in forward and reverse directions, and therefore there is a tendency for the motor-driven apparatus to creep in the direction of best operation because of the inability of the motor to return the apparatus to its starting condition when equal periods of time are allotted to reverse and forward rotations.

The motor 2 may be a shunt Wound direct current motor, or any other suitable reversible motor, and may have an armature 2a whose brushes 2b and 2c are connected respectively to two movable contactors 6 and 8 of an electromagneticallyoperated reversing switch I0. The contactors 6 and 8 are engageable with fixed switch contacts I2 and I4 respectively or, alternatively, with fixed switch contacts I6 and I8 respectively, The movable contactors 6 and 8 are normally spring biased into engagement with the contacts I2 and I4 (see drawing), but are moved counter to said spring bias upon the energization of the relay coil 20. The fixed contacts I4 and I6 are connected to one conductor 22 of the power line, while the fixed contacts I2 and I8 are connected to the other conductor 24 of the power line. It will be seen that energization of coil 20 of reversing switch I0 will effect reversal of the direction of operation of motor 2 by reversing the connections of the armature 2a to the power line 22, 24.

4In order to cause intermittent energization of the coil 20 for predetermined periods which are adjustable as to duration, I have provided a rotating commutator 26 comprising an insulating dise 28 having a conductive segment 30 of predetermined angular length, exceeding by, say, 10 to 30 degrees. The significance of this dimension will become apparent hereinafter,

The periphery of the rotating commutator 26 is engaged by a fixed brush 32 and by an arcuately adjustable brush 34. No structure for supporting the brushes 32 and 34 has been illustrated since such structure does not constitute a part of my invention, and since suitable devices for this purpose are well known in the art. 'I'he fixed brush 32 may be connected to line conductor 22 while the adjustable brush 34 may be connected to one terminal of relay coil 20. The other terminal of coil 20 is connected to line conductor 24, and consequently when both the brushes 32 and 34 contact the periphery of the conductive commutator segment 30 the relay winding 20 is energized from the line 22, 24, and movable contactors 6 and 8 are drawn, against their spring bias, into engagement with the fixed contacts I6 and I8 respectively. When one of the brushes,

32 or 34, is in contact with the periphery of the 'trolled by the rotating commutator 26, through the agency of the reversing switch III.

It wil1 now be apparent that the angular position of the brush 34 may be adjusted so as to vary relatively the periods of forward and reverse rotation of the motor 2. In this manner, the normally expected creep of the motor 2, and hence of the apparatus 4 driven by the motor 2, may be compensated for, so that the said apparatus may be caused to return on reverse rotation of the motor to exactly the same position from which it started. Or, if desired, the adjustment may be such as to cause a predetermined creep in either direction. The adjustable brush 34 may therefore be conveniently referred to as a creep control device, and is so designated in the drawing.

The apparatus hereinbefore described is particularly useful in connection with the operation of radio signaling apparatus of the type in which a directional antenna is caused to oscillate through a predetermined angle so as to scan a. certain sector, for example the sector designated S1 in the drawing.

For continuously rotating the control switch 30, a variable speed motor 36 may be employed, having, for example, an adjustable resistance device 38 in circuit therewith for varying the speed of the motor and hence the speed of rotation of the rotating commutator 26. In this manner, the periods of forward and reverse rotation may be lengthened or shortened, and the angle of the scanning sector correspondingly varied. Thus, for example, if the sector S1 is being scanned, it is readily possible, by reducing the speed of the motor 36, to increase the amplitude of oscillation of the scanning device 4 to that designated by the sector S2. The speed control rheostat 38 may therefore be conveniently referred to as the sector-amplitude control, and is so designated in the drawing. y

Under some conditions it may be desired to stop temporarily the rotation of the rotating commutator 26 Withoutstopping the variable speed motor 36. .For example, assume that the sector Si, to the north, is being scanned, and that for some reason-e. g. movement of the target-it is desired to scan the sector S3 to the southeast. While it is possible to effect this change in sector by a suitable adjustment of the creep control brush 34, it may be more rapidly effected by stopping the rotation of the rotating commutator 26 and permitting the motor 2 to operate in a given direction until the scanning device 4 reaches the desired sector, normal operation -being thereafter resumed.

In order that this may be readily accomplished, I prefer to insert a friction clutch 40, of any suitable type, in the mechanical drive system between the motor 36 and the rotating commutator 26, and to provide means for blocking or stopping the rotation of the said commutator. A preferred form of stopping device comprises means for stopping the rotating commutator 26 either in the position shown, which is characterized in that -both of the brushes make contact with the conducting segments 30, or .in a position which is characterized in that at least one of the brushes is out of contact with segment 30. In the first of said positions the motor 2 will rotate the scanning device 4 continuously in one direction, while in the second of said positions the scanning device will be rotated continuously in the opposite direction. AThe utility of such an arrangement will be understood if we assume that it is desired to effect a change in the general direction of scanning, say from the northern sector Si to the southeastern sector S3. It will be evident that this change can most quickly be effected by causing the scanning device to rotate fro-m sector S1 to sector S3 in a clockwise direction. However were it desired to scan a southwestern sector, or a western sector, such change would be most quickly effected by causing the scanning device to rotate from the sector Si in a counter-clockwise sense.

A suitable embodiment of a commutator stopping device capable of effecting such sector changes is illustrated diagrammatically in the drawing. The said device comprises an escapement-like element 42, pivoted about the pin 44,

and arranged cooperatively -with respect to a projecting stop 46 which is fixed on the face of the rotating commutator 26 and near the periphery thereof. The element -42 carries a pair of stop surfaces 48 and 50 arranged to engage the stop 46 and thereby to stop the rotation of the commutator 26. The stop surfaces 48 and 50 may be selectively moved into engagement I with the stop 46 by rotation of the element 42 about its pivot 44. Such movement of element 42 is conveniently effected by manipulation of a suitable handle 52. In radar sector scanning systems changes in sector are frequently made in changing from one object, or target, to another, and consequently the device 42 has been referred to as a target selector and it has been so designated in the drawing. Other forms of the target selector" will be apparent to those skilled in the art, and it is to 'be understood that my invention is not to be taken as limited to the specific design illustrated in the drawing.

Reference has been made hereinbefore to the angular extent of the conducting segment 30 of the rotating commutator 26. In general it is the object of the creep control device to provide a means whereby the relative periods of forward 'and reverse operation of the motor 2 may be varied within certain predetermined limits. More or less centrally stationed between these limits is preferably the condition in which the periods of forward and reverse operation of the motor are equal. If the conducting segment 30 occupied only of the peripheral surface of the device 26, it would be possible to secure a range of variation on only one side of the condition where the period of forward operation was equal to the period of reverse operation. With a 180 segment,` substantial equality of forward and reverse running periods would occur only if the brushes 32 and 34 were very small physically and disposed one immediately adjacent to (but not contacting) the other. From this it will be evident that if a range of variation is desired on yboth sides of the condition of equal running time it is necessary to employ a segment 30 occupying more than 180.

By means of the circuit arrangement and combination of elements hereinbefore described, the opening and closing of the reversing circuit of the motor 2 will be effected at the contacts I2, I4, I6 and I8 by movement of the contactors 6 and 8. All of these elementsmay be constructed and designed to withstand repeated openings and closings in a circuit having voltage and current values corresponding to the motor employed, as will be readily understood by those skilled in the art. Likewise, the rotating commutator 26 can readily be constructed and designed to operate under the voltage and current conditions incident to the repeated energization and deenergizatin of the relay coil 20, Since the two sets of conditions just mentioned are quite different, it will beobvious that more eilective design can be employed, and more efficient operation of the apparatus obtained, with the circuit and apparatus combination herein disclosed, than is possible with the prior arrangement hereinbefore mentioned. For example, it will be apparent that a relatively low voltage can be used to energize coil 20, thus substantially eliminating any sparking tendency at the periphery of the rotating commutator 2B.

In the drawing, the mechanical coupling means between the motor 2 and the scanning device 4, as well as between the motor 36 and rotating commutator 26, has been indicated diagrammatically by dashed lines drawn therebetween. It will be understood that conventional coupling devices may be employed, speed reduction gearing being utilized if necessary to provide proper operating speeds. Similarly, in the interests of simplicity, I have also omitted the various line switches which would normally be provided for cutting oi one or all of the elements of the system illustrated.

By way of example, in one satisfactory embodiment of the present invention, the speed of rotation of the commutator 26 was adjustable between limits of approximately 20 and 60 R. P. M. The speed of rotation of the motor 2 was so related that the scanning device 4 could be made to scan sectors of from 20 to 120.

Many modifications within the scope of my invention will occur to those skilled in the art. It is to -be understood, therefore, that I do not limit my invention to the arrangement and embodiment herein described and illustrated.

I claim:

1. An apparatus for controlling areversible motor, comprising a reversing switch, connections controlled by said switch to operate said motor in forward or reverse direction, electricallyoperable means for actuating said switch, powerdriven switching means for controlling the energization of said actuating means, thereby to control said reversing switch, means for adjusting said switching means to vary the relative duration of forward and reverse rotation of said motor, and means including a detent mechanism for stopping said switching means in a predetermined position to continue the operation of said motor in one direction.

2. An apparatus for controlling a reversible motor, comprising a reversing switch, connections controlled by said switch to operate said motor in forward or reverse direction, electrically-operable means for actuating said switch, powerdriven switching means for controlling the energizatlon of said actuating means, thereby to control said reversing switch, a friction clutch coupling between said switching means and its source of driving energy, and means to stop said switching means in either of two selecta-ble positions to continue the operation of said motor in one direction depending upon the selected position of said switching means.

3. A reverse switching system for an electrical device, comprising a rotary device having a segmental contact, a stationary brush and an adjustable brush engageable by saidsegmental contact, said adjustable brush being arcuately-movable to vary the period of joint engagement of said segmental contact with said brushes, and an electromagnetically-operated reversing switch controlled and operated yby the engagement of said segmental contact with said brushes for varying the connections of said electrical device to its supply source.

4. A reverse switching system for an electrical device, comprising rotary means having segmental contact means mounted to rotate therewith, stationary contact means and an adjustable contact means engageable by said segmental contact means, said adjustable contact means being arcuately-movable to vary the period of engagement of said segmental contact means with said other contact means, and an electromagnetically-operated reversing switch operated by the en- -other contact means, and an electromagnetically-operated reversing switch operated by the env gagement of said other contact means by said segmental contact means, said electromagnetic switch being normally biased, when deenergized, for completing a circuit to conduit current in one direction from a power source to said electrical device, and upon energization completing a circuit to conduct current in the opposite direction to the electrical device.

6. An apparatus for controlling a reversible motor, comprising a reversing switch for varying the connections of said motor to its supply source,

electromagnetic actuating means to move said ,p

switch to one position, biasing means to move the switch to another position when said electromagnetic means is deenergized, and a switch controlling the' energization and deenergization of said electromagnetic means, said last-named switch including a rotary contact, contact means engageable by said rotary contact to complete a circuit to said electromagnetic means, said contact means being adjustable to vary the relative duration of forward and reverse rotation of said motor.

7. An apparatus for controlling a reversible motor, comprising a reversing switch for varying the connections of said motor to its supply source, electromagnetic actuating means to move said Aswitch to one position, biasing means to move the switch to another position when said electromagnetic means is deenergized, and a switch controlling the energization and deenergization of said electromagnetic means, said lastnamed switch including a rotary contact, contact means engageable by said rotary contact to complete a circuit to said electromagnetic means, said contact means being adjustable to vary the relative duration of forward and reverse rotation of said motor, and a variable speed electric motor for driving said lastnamed switch at predetermined rates of speed.

8. An apparatus for controlling a reversible motor, comprising a reversing switch for varying the connections of said motor to its supply source,

electromagnetic actuating means to move said switch to one position, biasing means to move the switch to another position when said electromagrotation in a desired direction while said stopping means is maintained active.

9. An apparatus for controlling a reversible motor, comprising a reversing switch for varying the connections of said motor to its supply source, electromagnetic actuating means to move said switch to one position, biasing means to move the switch -to another position when said electromagnetic means is deenergized, and a, switch controlling the energization and deenergization of said electromagnetic means, said last-named switch including a rotary contact, contact means engageable by said rotary contact lto complete a circuit to said electromagnetic means, said contact means being adjustable to vary the relative duration of forward and reverse rotation of said motor, a variable speed electric motor for driving.r said rotary switch at predetermined rates of speed, and means to stop the rotation of said rotary switch while said first motor is running forward or reverse as desired, to continue the motor rotation in a desired direction while said stopping means is maintained active.

10. An vapparatus for controlling a reversible motor, comprising a reversing switch for varying thev connections of said motor .to its supply source, electromagnetic actuating means to move said switch to one position, biasing means to move the switch to another position when said electromaga netic means is deenergized, a switch controlling the energization and deenergization of said electromagnetic means, said last-named switch including a rotary contact, contact means engageable by said rotary contact to complete a circuit to said electromagnetic means, said contact means being adjustable to vary the relative duration of forward and reverse rotation of said motor, a variable speed electric motor for driving said rotary switch at predetermined rates of speed, a friction clutch connection between said driving motor and said rotary switch, and means to stop the rotation of said rotary switch while said first motor is running forward or reverse as desired, to continue the motor rotation in a desired direction while said stopping means is maintained active.

11. Apparatus for actuating a rotatable device back andforth through different sectors, comprising a reversible motor connected to said device to drive the4 same, electrically-operable means for effecting reversal of operation of said motor, power-driven switching means for controlling the operation of said reversing means, and means `including a detent mechanism for stopping said switching means to eiect; change of the sector through which said device is actuated.

12. Apparatus for actuating a rotatable device back and forth through different sectors, comprising a reversible motorl connected to said device to drive the same, electrically-operable means for eiecting reversal of operation of said motor, power-driven switching means for controlling thev operation of said reversing means,

means for varying the speed of operation of said switching means to vary the amplitude of the sector through which said device is actuated, and means including a detent mechanism for stopping said switching means to eiect change of the sector through which said device is actuated.

13. Apparatus for actuating a rotatable device back and forth through different sectors, comprising a reversible motor connected to said device to drive the same, electrically-operable means foreiecting reversal of operation of said motor, power-driven switching means for controlling the operation of said reversing means, means for varying the speed of operation of said switching means tol vary. the amplitude of the sector through which said device is actuated, means for adjusting said switching means to vary the relative duration of forward and reverse rotation of said motor, and means including a detent mechanism for stopping said switch- I ing means to effect change of the sector through which said device is actuated.

14. In combination, a rotatable scanning device to be actuated back and forth through a desired sector, a reversible motor connected tosaid device to drive the same, electrically-operable means for effecting reversal of operation of said motor, power-driven switching means for controlling the operation of said reversing means, and means for adjusting said switching means to vary the relative duration of forward and reverse operation of said motor so as to compensate for any creeping of said scanning device due to inherent tendency of said motor to run better in one direction than in the other.

MALCOLM G. SHOEMAKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 845,831 Watson Mar. 5, 1907 1,882,819 Hanneman Oct. 18, 1932 2,310,335 Wolfson Feb. 9, 1943 

